How can I cope with grief and feelings of guilt after my husband's death?

A month ago my husband (86) passed away. He had had health problems for a long time (although apparently not serious illness). He could hardly walk with a walker, slept a lot, hardly ate and had lost a lot of weight. I have rheumatoid arthritis and lupus, but being his only caregiver I took care of him the best I could. He had many bladder and bowel accidents, and I would spend some nights cleaning him and changing his clothes and bedding. So one day I prayed the Lord to take him, but immediately I felt bad and added that only if it was His will and if it wasn't something that I would regret afterwards. In the last months it became harder for me to take care of him, and take him to doctors' visits, so when a nurse suggested home hospice care and explained that I would have help with him and I wouldn't have to take him to the doctors since he would have nurses and home help providers come to the house, I thought it was convenient. I loved my husband but I was feeling completely exhausted,

Two days before his death he had a very serious constipation problem. I gave him a tablet prescribed by the nurse, but since he refused to drink much water; it didn't work. That night he was struggling a lot (I felt so sorry for him), so I gave him another tablet with a full glass of water. A little after, he went to the bathroom and had a bowel movement (we both felt relieved), but later he started having terrible diarrhea and later he started to vomit a black liquid. Lots of it. I got scared and called hospice, but it was a long time before the nurse came. She then said he needed to to be taken to the hospice installations. When we got there the head nurse told me they would keep him there for a couple or three days, so I assumed his condition was not so critical. He kept saying he wanted to go back home, and complaining of feeling very cold. They added some blankets, but he insisted he wanted to go home. I told him to be patient, that he needed to stay so he could get better. Since I had not slept for two days I thought it was OK for me to come home and sleep. The following morning when I got there I and my daughter tried to wake him up. His mouth was wide open and he was breathing heavily and did not respond to us. The nurse told us he had had a very bad agitated night and had been vomiting a lot of the black liquid (I understand it was blood). She told me they had sedated him. I asked her if that was the reason he couldn't wake up, but she said that the medication should have worn off a long time before. We were at his side all day and his breathing pattern changed, and then there was a gurgling noise coming from his chest. He died at noon.

I am being tormented by my grief and my feelings of guilt: first, because I had prayed some time before for God to take him and second, because I didn't spend that night at his side.

Another thing that is tormenting me is that I can't understand why, just one day before he was conscious and talking, and the next day he died. I didn't receive an explanation for the cause of his death.

Now I feel so miserable. I feel so sad and lonely without him. I miss him terribly. The house feels so empty without him. I feel I am in deep depression (and I'm taking medication for it). If I could go back in time, I would have him back with me, even if I had to take care of him the way I was doing it.